Regulating circuits



06L 4, 1932- R. w. CHESNUT ET AL 0 REGULATING CIRCUITS Filed June 26,1929 3 Sheets-Sheet 1 IIIML lNVE/VTORS. R. W CHESNU T D M TEIFPRY W EKANNENBEHG A TTOFPNE 3 1932- R. w. CHESNUT ET AL 1,380,390

REGULATING C IRCUITS Filed June 26, 1929 3 Sheets-Sheet 2 (20%) (40%)(BC/b) (120%) lilaN-loCklN Q/THRH P05. 1(5) /5 H. V14 CHES'NUTlNl/ENTORS I D M- TERRY I/M F. KANNENBERG Oct. 4, 1932.

R. W. CHESNUT ET AL REGULATING CIRCUITS Filed June 26, 1929 3Sheets-Sheet 3 R W CHESNUT D.M TER'FPY V14 F: KANNEAIBERG A TOR/VEVPatented Oct. 4, 1932 ROY W. CHESNUT, OF UPPER IvIONTCLAIR, NEW JERSEY,DONALD M. TERRY, 0F ELM- HURST, NEW YORK, AND HALTER F. KANNENBERG, OFLYNDHURST, NEW JERSEY, ASSIGNORS TO BELL TELEPHONE LABORATGRIES,INCORPORATED, 013 NEW YORK,

N. Y., A CORPGRATIGN N EW YORK BEGULATING CIRCUITS Application filedJune 26,

This inventionrelates to electrical transmission systems and moreparticularly to means and methods whereby the transmission efiiciency ofa system may be maintained substantially constant.

'Where a plurality of signals are simultaneously transmitted over acommon conducting system through the agency of carrier currents ofdifferent frequencies, it is desirable that the attenuation of thecarrier system as regards the several frequencies be maintainedsubstantially constant regardless of the oranges in the line conditions.Changes in the attenuation of a system of this character are due to avariety of causes but arise principally from variations in the leakagecondition of the open-wire lines employed as conductors, the attenuationbeing much greater during wet weather than during dry weather. Thissource of variation in the transmission efficiency of the system isquite distinct from the usual causes of transmiss on variations in longcable circuits operated ordinary telphone frequencies where theresistance variation with temperature is a controlling factor.

One of the objectsof this invention is to provide means and methodswhereby in a system for the transmission of signals, the transmissionefficiency of the circuit may be automatically maintained substantiallyconstant under various conditions.

Another object of this invention is to provide means and methods wherebythis result nay be obtained through the agency of a pilot frequencywhich is subjected to the changes in line conditions which affect thefrequencies employed for signaling, so that elements of the circuit maybe adjusted to off set the attenuation changes indicated by the pilotfrequency.

Another object of the invention is to provide means and methods wherebyselecting app aratus is automatically operable in response to the charges in the current from the pilot indicater to set up electrical pathsin the adjusting system and to periodically transmit current through thepaths so set up to efiect the desired ad ustment to maintain thetransmis- 1929. Serial No. 373,762.

sion eiiiciency of the circuit substantially con stant under variousconditions.

The invention is applicableto any type of transmission system whoseattenuation is subj ect to change, but it has especial application tomultiplex carrier transmission systems and the detailed description willrefer specifically to such a system.

In general the operation of the system is as follows:

The pilot currents which operate the automatic gain control circuit andthe speech side band currents come in from the high frequency line andpass through directional filters, equalizers and other apparatus andthen through a variable artificial line which is controlledautomatically.

The automatic control circuit cuts in or out the proper number of unitsin the variable artificial line which attenuates the pilot current andthe speech side band currents the proper amount so that when they areamplified in the receiving amplifier, the proper current level output ornormal current level is maintained. From the output of the amplifier thepilot indicator current is transmitted to the input of the automaticgain control circuit.

The speech side band currents are separated the output of the amplifierfrom the pilot channel current and pass through their respective bandfilters. The pilot current is selected by tuned circuits and rectifiedin a vacuum tube to give direct current. The amount of this directcurrent varies with the amount of the pilot current arriving so that ifthere are not sufiicicnt'units cut into the variable artificial line therectified direct current will be too large. On the other hand if toomany units are cut into the variable artificial line the rectifiercurrent produced will be too small. This direct current is automaticallyused to cut out or in units until it adjusts itself to the desirednormal level.

This adjustment is effected in the following manner. Current from apilot indicator passes through an indicating controller.

his controller consists essentially of a galvanometer through whichcurrents from the pilot indicator are transmitted and a small motorwhich causes the galvanometer pointer to be depressed at 15-secondintervals. If the galvanometer indicates normal transmission level, thegalvanometer pointer does not cause any of the contacts associated withthe galvanometcr to close when the pointer is depressed. If, however,the transmission level is other than normal,the galvanometer pointerwhen depressed, causes one of three contacts to close, depending on themagnitude of direct current flowing through the galvanometer. Anadditional pair of contacts, which will hereinafter be referred to asthe trigger contacts, are closed by means of a cam arrangement operatedby the same motor referred to above for approximately one-half second,approximatel ten seconds after the pointer has been depressed. In theinterval while the galvanometer pointer is not depressed it is free tomove depending on the amount of current flowing in the galvanometer.

One of the three contacts which are under the control of the pointer isused for alarm purposes only and will be referred to in connection withthe alarm circuit which will be described later. The other two contactsare used for the automatic regulation. If the current value is too highthe high contact makes. If it is too low the low contact makes and ifthe current value is at the proper or normal level neither of saidcontacts will make.

The high and low contacts, when made, set up electrical paths throughautomatic selectors. The trigger contact later sends current throughthese paths to change the amount of. attenuation in the variableartificial line. If the current is at the normal level so that neitherof the high or low contacts makes, the automatic selectors do not changeand the trigger contact sends current through the sai e paths as beforeand does not change the setting of the variable artificial line.

The various provisions of the invention for performing these functionsand for carrying out the various objects will now be described inconnection with the accompanying drawings to which reference will bemade.

In the drawings Figs. 1 to 3, when placed above each other with Fig. 1at the top, show in schematic form the circuit arrangements of arepeater station and associated automatic gain control system accordingto the invention, and Fig. 1A shows the method employed to operate oneof the contacting devices on the indicating controller by a camarrangement which periodically causes the pointer on the indicatingcontroller to move downward.

General signal transmission circuit Reference will first be made to thegeneral arrangement of the signal transmitting system, the line ML beinga multiplex carrier line extending in both directions from the repeaterstation shown in Fig. 1 and tenninating at each of two stations. Carrierwaves of distinctive frequencies may be used for effecting exclusivecommunication between corresponding sets in the usual manner. Inaddition to the signaling sets a pilot channel is also associated withthe line ML in the usual manner, the pilot channel using a wave of afrequency distinct from the carrier frequencies of the signalingchannels. The carrier waves and the pilot frequency waves from the eaststation, not shown, are transmitted over the line ML to the repeaterstation shown. These waves are transmitted through the east-west filter1, the east-west equalizer 2, line section 3, transformer 4, linesection 5, attenuation equalizer 6, line section 7, east-west amplifier8, line section 9, east-west filter 10 and line ML to the west stationnot shown. Signal carrier waves and the pilot frequency from the weststation are received over the line ML, west-east filter 11,

west-east equalizer 12, line section 13, automatic gain control circuit14, line section 17, west-east amplifier 18, line section 19, westeastfilter 20 and line ML to the east station.

The complete carrier system and the repeater station may be constructedin the manner well known in the art. They may for example be constructedin accordance with the disclosure in the Bell System Technical Journalvol. VII, pp. 564629, July 1928, entitled Carrier Systems on LongDistance Telephone Lines by H. A. Atfel, C. S. Demarest and C. W. Green.

The filters 1, 10, 11 and 20 may be constructed in accordance with theusual practice for carrier current transmission systems. These filtersmay, for example, be constructed in accordance with the disclosure in U.S. Patent No. 1,227,113 to Campbell, May 22, 1917. The equalizers 2 and12 may, for example, be constructed in accordance with U. S. Patent No.1,603,305, to Zobel, October 19, 1926. The seven units, 21 to 27inclusive, of the attenuation equalizer 6 may be constructed in anyknown manner, as for example, in accordance with the disclosure in U. S.Patent No. 1,511,013 to Atfcl, October 7, 1924:. The amplifiers 8 and 18may be constructed in the manner well known in the art. The automaticgain control circuit 14 ably constructed similar to the equalizer unit21.

Relays 31 to 37 inclusive are employed to operate switches, to insertthe des" d nunr ber of attenuation units 21 to 27 inclusive between linesections 5 and 7, to control the current amplitude transmitted toamplifier Relay 31 controls switches 33 and 39 which are associated withthe attenuation unit 21 Switch 38 when closed as shown, connects shuntelement 28 oi attenuation unit 21 from one side of line section 7 to themi eint of the series elements of the attenuation unit 21. When relay 31is operated, switch 38 opens and switch 39 closes. ll hei switch opens,the shunt element 28 is disconnected from line section 7 and when switch39 closes, a circuit is completed from the connection 40 between theseries elements of attenuation units 21 and 22, through switch 39 to theother side of line section 7 at 41, which effectively shunts out theseries elements or" as tenuation unit 21. In this manner the attenuation unit 21, which when the relay 31 is unoperated, as shown, isconnected between line sections 5 and 7, can be disconnected frombetween line sections 5 and 7 by the operation of relay 31.

Relay 34 controls switches 42 and 43 which are associated with theattenuation equalizer unit 24. Switch'42 when closed, as shown, connectsthe shunt element 44 in the circuit, in a manner similar to switch 38 onrelay 32 in connection with equalizer unit 21. When relay 34 isoperated, switch 42 opens and switch 43 closes. Switch 42, when opened,disconnects the shunt element 44 from the circuit and switch 43 whenclosed, completes a circuit from the connection 46, between attenuationunits 24 and 25 through switch 43, to the connection 47, bet-weenattenuation units and 24, thereby etlectively short-circuiting theseries element 45. llelays 32, 33, 35, 36 and 37 in a like mannercontrol their associated attenuation units 22, 23, 25, 26 and 27.

In the system illustrated the attenuation units 21 to 27 are constructedto provide the following transmission loss: 21- A db, 22 db, 23-1 db,242 db, 254 db, 26-8 db, 2712 db. Since any combination of theseattenuation units may beinserted between line sections 5 and 7, theattenuation may be varied from zero to 27% db, in db steps.

Manual control of the attenuation eguale'e'er to its upper position, acircuit is completed from ground through switch 57 relay 56 and battery58 to ground which operates relay 56. When relay 56 operates, switch isopened and switch 59 is closed. When switch 59 is closed, a circuit iscompleted from ground through switch 59, switch 48, switch 52 of key 15,right hand winding of relay 34 and battery 53 to ground, which operatesrelay 34, thereby closing switch on relay If, after relay 34 hasoperated, 56 is released by the opening of switch I circuit will becompleted from ground ugl battery 53, left hand winding of reswitch 54and switch 55 to ground, there y holding relay in its operated position.This is accomplished by adjusting switches 55 and 59 so that when relay56 re leases, switch 55 will close before switch 59 opens.

To release relay 34 it is only necessary to close switch 57 momentarilywith switch This will operate relay 56 as del thereby opening switch 55and =5 s I ch 59. The closing of switch 59, 1 switch 48 open, will notenergize the hand winding of relay 34 and when switch subsequentlyopens, the circuit is broken through the left hand winding of relay 34and it will release.

in a simila manner relays 35, 36 and 37 may be oper ed by tl e momentaryclosing of switch 57 with switches 49, 50 and 51 closed an d may bereleased in the manner described above in connection with relay 34.

Relays 31, 32 and 33, as shown, are aranged to operate whenever switch57 of key 5 is closed, as they are connected in a manner similar to reays 34 to 37 inclusive, except that switches similar to 48 to 51inclusive have not been provided to break the circuits through the righthand windings of relays 3 to 33 inclusive. Relays 31 to 33 inclusivemay, however, also be operated and released by providing additionalswitches, not shown, connected in a manner similar to switches to 51inclusive.

Since either one or all switches 48 to 51 may be opened or closed at thesame time that the switch 57 is momentarily closed, any combination ofthe relays to 37 inclusive may be operated and/or releasedsimultaneously.

Automatic control of attenuation equaliser Part of the currents from theoutput of amplifier 8 are shunted from the line section 9 over linesection 60, through transformer 61 to the tuned circuit 62. tuned to,the pilot frequency and effectively suppresses the signal frequencieswhich are transmitted through amplifier 8. The pilot frequency currentsare transmitted through the tuned circuit 62 to a rectifier 63. Thedirect current from rectifier 63 is transmitted through a visualindicating meter 64, and line section 65 to an indicating controller 66.Since, as stated above, the currents are transmitted through thevariable attenuation equalizer 6 before reaching the amplifier 8 theamount of direct current transmitted through meter 64 to the indicatingcontroller 66 can be controlled by varying the number of attenuationequalizer units 21 to 27 inclusive through which these currents mustpass.

Description of operation of indicating controller The indicatingcontroller 66 comprises a galvanometer unit 67 having a pointer 68 whichmoves along the face 69 as the current through the galvanometer 67changes. A motor 70 drives a shaft 71 to which are rigidly fixed cams 72and 73. As cam 73 revolves the rod 74 is moved upward (toward thereader, in Fig. 1) for a short interval at approximately 15secondintervals, causing a bar 75 which is pivoted at points 300 and 301 tocome in contact with the pointer 68 and move the pointer 68 downward(away from the reader, in Fig. 1).

Three contacting devices 76, 77 and 78 are arranged along the face 69and beneath the pointer 68. When the pointer 68 is directly over thecontacting device 76 (referred to above as the high contact) at the timethe bar 75 depresses the pointer 68, the projection 79 on the pointer 68closes the circuit from ground to conductor 80. If the pointer isdirectly over the contacting devices 77 (referred to above as the lowcontact) or 78 at the time that the pointer 68 is depressed, the circuitfrom ground through these contacting devices 77 or 78 will be closed ina similar manner to that shown for contacting device 76.

Fig. 1A shows in detail the manner in which the contacting devices 76,77 and 78 are momentarily closed by the action of cam 73. When the cam73 is in the position shown the pointer 68 is free to move under controlof the galvanometer 67, as the pointer 68 is not in contact with the bar75. The bar 75 has a yoked portion 305, which yoke extends around thebar 75 between the head 306 and collar 307, which head and collar arerigidly fastened to the rod 74. The bar 75 is supported by the pivots300 and 301, which pivots are rigidly fastened to supports 308 and 309.

This circuit 62 is 1-A), toward the pointer 68. When either of theprojecting portions 302 or 3030f the cam 73 come in contact with the Lshaped member 304, which is attached to the rod 74, the rod 74 is movedupward, allowing the portion of the bar 75 to the right of pivot 300 tomove downward against the pointer 68 and to move the pointer 68 downwardwith it.

If the pointer is directly over the contacting device 76, as shown inFig. 1A, the projection 79 causes the contacting device 76 to close thecircuit from ground to conductor 80.

WVhen the cam 73 has moved so that neither projecting portion 302 nor303 is in contact with the member 304 the weight of the rod 74 moves thebar 75 away from pointer 68 and the spring 310 causes the contactingdevice 76 to open the circuit from ground through conductor 80.

The cam 72 is arranged to close switch 81 (referred to above as thetrigger contact) for approximately second, approximately eight secondsafter the pointer 68 has been depressed and returned to a sufiicientheight so that the contacts 76, 77 or 78 will have opened.

The contacting devices 76 and 77 are arranged so that when the pointer68 is directly over the space between these contacting devices thedepression of the pointer will not cause the operation of either ofthem. The contacting device 78 is arranged, with respect to contactingdevice 77, so that there is no space between these contacts, in orderthat the contacting device 78 will be operated whenever the pointer isto the left of contacting device 77.

When the indicator 68 is between the contacting devices 76 and 77, asshown, the current level at the output of amplifier 8 is at the desiredor normal level. hen the current level is higher than normal the pointer68 is moved by the galvanometer 67 over contacting device 76, and whenthe current level is lower than normal the pointer 68 is moved overcontacting device 77 or 78. The contacting device 78 is provided foralarm purposes and will be referred to later In general the function ofcontacting devices 76 and 77 is to control the operation of automaticselectors A1 to A5 inclusive, (Fig. 3), B1 to B6 inclusive and C1 to C6inclusive, in order that the proper circuits may be completed throughrelays 31 to 37 inelusive.

lVhen the cam 72 closes switch 81, a circuit is completed from groundthrough switch 81, conductor 82, switch 83 on relay 84, (Fig. 3),

115 inclusive.

conductor 85, switch 86 on key 15, conductor 87, relay 56 and battery 58to ground.

This will operate relay 56 in a manner similar to its operation byswitch 57 as described above and hold up any of the relays 31 to 37Operation of selector switches Selector switches A1 to A5 inclusive areoperated by the magnet A, selector switches B1 to B6 by the magnet B andselector switches C1 to C5 inclusive by the magnet C.

The five contact arms 91 to 95 inclusive of the selector switch A, ifdesired, may be mounted on a common shaft. Likewise the sin contact arms96 to 101 inclusive of the selector switch B may be mounted on a commonshaft and the five contact arms 102 to 106 inclusive of the selectorswitch C may be mounted on a common shaft. The step-bystep mechanismsfor the contact arms are not shown in the drawings, but may be ofsuitable type, and each may comprise, for example, a ratchet wheelmounted on the shaft and controlled by a stepping pawl adjacent to themagnets A, B and G, in a manner well known in the art. These contactarms will be controlled by their stepping mechanisms in such a manner asto cause them to rotate in a counter-clockwise direction.

Slow-release relay 88 is associated with selector magnet A to retard thespeed of opera-tion of the magnet A. Belay 89 is associated withselector magnet B to lock up when a pulse is received by the selectormagnet B until the selector magnet B has completely operated. Belay 90is associated with selector magnet C for the same purpose that relay 89is associated with selector magnet B.

lVith the switch arms in the position shown, when the switch 81 isclosed by the cam 7 2, which causes the operation of relay 56 asdescribed above, the closing of switch 59 on relay 56 completes acircuit from ground through switch 59, conductor 107, switch arm 99 andcontact 108 on the B4 selector switch, conductor 109, right hand windingof relay 31 and battery 58 to ground. When the relay 56 is released, dueto the opening of switch 81 by the action of cam 72, relay 31 is lockedup through its left hand winding in the manner described above. In asimilar manner relays 32 to 37 inclusive are operated through selectorswitch arms 100, 101 and 103 to 106 inclusive and their associatedselector switch contacts 110 to All the attenuation units 21 to 27inclusive will then be removed from between line sections 5 and 7 afterthe switch 81 is closed because relays 31 to 3'? are all energized.

When the B1 to B6 selectors are stepped forward one step, in thedirection indicated, by the selector magnet B the switch arm 99 of theB4 selector steps to the idle contact 316, which opens the circuitpreviously existing over conductor 109. The subsequent operation andrelease of relay 56 will cause relay 31 to release and connect theattenuation equalizer unit 21 between line sections 5 and 7. Sincecontacts 317 and 318 are engaged by switch arms 100 and 101, relays 32and 33 will remain operated. In this manner, as the selector switches B1to B6 are stepped forward and the relay 56 operated after each step, theattenuation is increased in 4 db steps from zero to 1- db. This requiresseven steps forward on the part of the B selector switches.

In order to increase the attenuation from 1% db to 2 db it is necessaryto step the B1 to B6 selector switches fifteen steps forward and to stepthe C1 to C5 selector switches forward one step. The subsequentoperation of relay 56 will remove attenuation units 21 to 23 inclusiveand insert attenuation unit 24. As the selector switches B1 to B6 areagain stepped forward as described above the attenuation increases in dbsteps from 2 db to 2- db. By again stepping the B1 to B6 selector switcharms to the position shown and stepping the C1 to C5 selector switcharms one step forward, the subsequent operation of relay 56 inserts theattenuation equalizer unit and removes the attenuation equalizer units21 to 24 inclusive. The further operation of the B1 to B6 selectorsinclusive and C1 to C5 selectors inclusive will increase the attenuationin 1; db steps under control of the contacting device 76 until a totalof 27 /1 db is reached.

In order to decrease the attenuation from 27 /4 db the B1 to B6 selectorswitches are moved forward one step less than a complete cycle and therelay 56 is operated as described above, which will reduce theattenuation to 27 db. There are 22 steps in acomplete cycle for the B1to B6 selector switches and for the C1 to C5 selector switches. In asimilar manner, by stepping the B1 to B6 selector switches forward onestep less than the complete cycle, the attenuation is reduced in ,1; dbsteps until 26 db is reached. At this point it is necessary to move theC1 to C5 selector switches forward 21 steps or one step less than acomplete cycle and to move the B1 to B6 selector switches forward 7steps, in order to reduce the attenuation to 25- db. In this manner theattenuation can be reduced in /4 db steps until zero attenuation isreached.

Operation of the automatic circuit 'When the pointer 68 of theindicating controller 66 is between the contacts 7 6 and 7 7 as shown,no one of the contacts 7 6, 7 7 or 7 8 will be operated by the action ofcam 73, and each time the switch 81 (referred to above as the 3 throughthe selector switch arms B1 to B6 inclusive and C2 to C5 inclusive asdescribed above. V

If some one or more of the attenuation units 21 to 27 inclusive areinserted between line sections 5 and 7 when the line conditions changeand the pointer 68 is moved over contact 76, the closing of contact 76by the action of cam 73 completes a circuit from ground through contact76, conductor 80, switch 116 of relay 117, switch 118 of relay 84,conductor 119, lower winding of relay 120, conductor 121, switch 122 onkey 123 and battery 124 to ground, thereby operating relay 120. Switch116 on relay 117 has been shown in an opened position. It will, however,be closed whenever any of the attenuation units 21 to 27 inclusive arecut out between line sections 5 and 7. The function of switch 116 andrelay 117 will be more fully explained below in connection with thealarm circuits.

When relay 120 operates, switch 125 closes,

completing a circuit from ground through battery 124,.switch 123,conductor 121, upper winding on relay 120, switch 125 on relay 120,

conductor 126 and switch 127 on relay 128 to ground, thereby holdingtherelay 120 in an operated position. Relay 120, when operated, alsocompletes a circuit from ground through contact 76 on the indicatingrecord- 2 er 66, conductor so, switch 116, switch 118,

conductor 119, switch 328, selector magnet B, conductor 121, switch 122and battery 124 to ground.

When the contact 76 is broken by the ac tion of cam 73 the selectorswitch arms 96 to 101 inclusive on the B selector are stepped forwardone step. The first sixsteps which the B selector takes are accomplishedin this same manner under control of galvanometer 66. When the selectorswitch arm 96 of the B1 selector is stepped from contact 129 to contact130 a circuit is completed from ground through switch 131 on relay 120,conductor 132, selector switch contact 130, selector switch arm 96,switch 133 on selector magnet B, selector magnet B, conductor 121,switch 122 and battery 124 to ground, thereby oper-' ating the selectorswitch magnet B which interrupts its own circuit at contact 133 andmoves selector switch arms 96 to 101 inclusive over the remainingselector switch contacts. The B selector switches will thus be steppedforward, to the position shown, which opens the circuit from selectorswitch arm'96 to conductor 132.

Relay 120 by being held in the operated position in the manner describedabove enables the B selector switches move more than one step forwardwhen switch 76 on the in dicating recorder 66 is closed even though theswitch 76 opens before the B selector switches have stepped forward tothe posi tions shown. Relay 120 also opens switch 134 which disconnectsrelay 89 from the circuit. Belay 89 has no function at this time. Itspurpose will be described later in connection with the operation of theA selectors which control the B selectors to increase the gain.

When the selector switch arm 97 on the B2 selector switch makes contactwith selector switch contacts 136 a circuit is completed from groundthrough battery 124, switch 336 of key 123, conductor 137, selectorswitch magnet C, conductor 138, selector switch contacts 136 on the B2selector switch, selector switch arm 97, conductor 139, selector switchcontact 140 on the A4 selector switch and selector switch arm 94 toground, which operates selector switch magnet C and relay 90 and stepsselector switch arms 102 to 106 inclusive one step forward. When relay90 operates, it closes switch 141 maintaining the ground connection tothe selector switch. magnet C until selector switch magnet C hascompletely operated and opened the switch 142, even though the selectorswitch arm 97 has been stepped beyond selector switch contacts 136before selector switch magnet C has operated.

lVhen the switch 81 is closed by the action of cam 72, a circuit iscompleted from ground through switch 81, conductor 82, switch S3,conductor 176, relay 128, conductor 177 and battery 178 to ground,thereby operating relay 128 and opening switch 127. When switch 127opens the locking circuit through relay 120 is broken, allowing relay120 to return to its normal. position.

In a similar manner the total attenuation between line sections 5 and 7can be increased in db steps as long as pointer 68 remains over thecontact 76.

l Vhen line conditions change and the indicating pointer 68 moves overthe contact 77, indicating that the attenuation of the attenuationequalizer is too large, the system operates to decrease the attenuationin /4 db steps by stepping the selector switch arms forward one stepless than a complete cycle as described above. This is accomplished bysupplying the proper number of stepping impulses to the B and Cselectors by means of selector switches A1 to A5 inclusive.

When the cam 73 causes switch 77 to close a circuit is completed fromground through switch 77, conductor 143, switch 144 on relay 145, switch146 on relay 84, conductor 147, switch 148 on relay 149, selector switchcontact 150 on the A1 selector switch, selector switch arm 91 onselector switch A1, switch 151 011 selector switch magnet A, relay 88,conductor 152, switch 153 on key 123 and battery 124 to ground, whichoperates relay 88, it being noted that relays 145 and 84 are nowenergized under control of switches 191 to 197 inclusive (Fig. 2) andthe A, B and 0 selectors (Fig. 3) respectively. When relay 88 operates,switch 154: closes, entendin previously traced lead fr in ground on contact 7'? to selector switch magnet A, conductor 152, switch 153 andbattery 12a to ground thereby operating the selector switch magnet A.When the selector switch magnet A opcrates, switch 151 opens the abovementioned circuit through relay 88 and relay 88 releases. When relay 88releases it opens switch 154 on relay 88, allowing selector switchmagnet A to release and rotate selector switch arms 91 to 95 inclusiveone step forward in the direction indicated.

' hen the selector switch arm 91 of the A1 selector switch is steppedforward it malzes contact with selector switci contact 155, completing acircui from "round through battery 12 1, switch 153 on key 123,conductor 152, relay 88, switch 151, selector switch arm 91 and selectorswitch contact 155 to ground, thereby operating relay 88. The operationof relay 88 operates selector switchesvAl to A5 inclusive an additionalstep forward as described above. Since all the selector switch contactson selector swi the sch A1, except contact 150, are connecteddirectly'to ground the above operation is re peated until selectorswitch arm 91 has stepped forward from the last selector switch contact156. Selector switch arm 92 of the A2 selector switch makes contact withselector switch 157 when selector switch arm 91 is stepped forward fromselector switch contact 156. The operation of relay 88 and se lectorswitch magnet B is repeated by the ground connection through theselector switch arm 92 until the selector switch arms 91 to 95 inclusivehave been stepped forward a complete cycle of 44 steps and returned tothe position shown.

As the relay 88 must operate between every step of the A selectorswitch, it slows down the operation of the A. selector switch, so thatthe current impulses received by the B and C selector switches from theA 1- and A5 selector switches will not be transmitted too rapidly.

l s hen the selector switch arm 98 of the 113 selector switch makescontact with selector sw tch contacts 158, a circuit is completed fromground through selector switch arm 93, selector switch contacts 158,conductor 159, relay 14:9, conductor 152, switch 153 and battery 12 1 toground, which operates relay 1 19. The operation of relay 1 19 opens theswitch 148, which opens the circuit from ground through the contactingdevice 'l'? on the indicating controller 66 and relay 88, therebypreventing the turther rotation of selector switch arms 91 to 95inclusive it the selector switch arm 91 makes contact with selectorswitch contact 150, before switch 77 has opened under the control of cam7 3. After switch 77 opens th closing of switch 81 operates relay 128,thereby opening the circuit through switch 127 and relay 149, relay 149releases and the system is in condition for the next' through selectorswitch arm 9 1, selector switch contact 160, conductor 161, selectormagnet B, conductor 121, switch 122 and battery 12 1 to ground, whichoperates the relay 89 and the selector switch magnet B in the mannerdescriied above, for relay 90 and selector magnet C, it being noted thatrelay 120 is d-eenergized at this time, allowing circuit of relay 89 tobe made through back contact 134.

The selector switch arms 96' to 101 inclusive on the B selector are thusstepped forward. when the selector switch arm 94 of the A4 selectorswitch contacts with every other selector switch contact for seven stepsat the conclusion of which the selector switch arm 94: is ii contactwith contact 162. After the selector switch arm 9-1 has contacted withselector switch contact 163, selector switch arms 96 to 101 inclusive ofthe B selector are stepped forward for fourteen additional steps in asimilar manner, except that the circuits from battery 124, through relay89 and selector switch magnet B are completed through selector switchcontacts 163 and each alternate succeeding contact on. the A 1 selectorswitch and through selector switch arm 95 and each alternate contact ofselector switch [15, conductor 16 1, and switch 165 on relay 166.

V7 hen the B selector switch arms 96 to 101 inclusive are on the firststep, in the position shown, and the switch 77 closed by the action ofcam 73, it is necessary that the B selector switch arms 96 to 101inclusive be stepped forward seven steps as described in the preced ingparagraph instead of the usual twentyone, but it is also necessary tostep the C selector switch arms 102 to 106 inclusive forward twenty-onesteps (which is one step less than a complete cycle) causing the Bselector to insert 1 db, db, and A db attenuation equalizer units andthe C selector to remove the 2 db unit.

This accomp ished as follows: VJ hen the A3 selector switch arm 93 movesforward one step from the position shown, switch arm 98 makes contactwith selector switch contact 167, comple ing a circuit from groundthrough selector switch arm 93, contact 167, selector switch arm 98 ofthe B8 selector, conductor 168, relay 166, conductor 152, switch 153 andbattery 124 to ground thereby oper ating relay 166. lVhen relay 166operates, switch 169 closes a circuit from ground through switch 127 onrelay 128, conductor 126, switch 169 on relay 166, relay 166, conductor152, switch 153 and battery 124 to ground, thereby holding relay 166 inits oper ated position.

As the selector switch 94 of the A4 selector makes contact with selectorswitch contact 171, and each alternate contact on the A4 selectorswitch, a circuit is completed from ground through selector switch arm94, conductor 172, conductor 138 through the selector switch magnet Cand relay 90, which operates the selector switch magnet C and relay 90as described above, and steps the selector switch arms 102 to 106inclusive of the C selector eleven steps forward (there being elevencircuit closures by arm 94). Two additional steps of the A selectorbrings selector switch arm 95 in contact with selector switch contact173, completing a circuit from ground through selector switch arm 95 andthe selector switch magnet G and relay 90, which steps selector switcharms 102 to 106 inclusive of the, C selector forward in the mannerdescribed above. This is repeated on each alternate contact of selectorswitch A5 for ten steps. The C selector switch arms 102 to 106 inclusivehave then been stepped forward twenty-one steps, or one less'than acomplete cycle. When selector switch arm 95 of the A5 selector switchcontacts with selector switch contact 174, as relay 166 has alreadyoperated to open switch 170 the selector switch arm 95 is prevented fromcompleting the circuit from ground through selector switch arm 95,conductor 175, switch 170, conductor 172, conductor 138 and selectorswitch magnet C and relay 90, which circuit it completed would step theselector switch arms 102 to 106 inclusive of the C selector forward anadditional step.

The operation of relay 166 also opens switch 165, thereby opening thecircuit from ground through selector switch arms 94 and 95, selectorswitch contacts on the A4 and A5 selector switches, conductor 164,switch 165, selector switch magnet B and relay 89 to bat tery 124,thereby preventing the selector switch arms 94 and 95 from operating theselector switch magnet B and relay 89, after selector switch arm 94 hasbeen stepped past selector switch contact 162. (There having alreadybeen seven circuit closures through the switch arm 94 and the selectorswitch magnet B as described above.)

The subsequent closing of switch 81 (the trigger contact) by the actionof cam 72 completes a circuit from ground through switch 81, conductor82, switch 83, conductor 176, relay 128, conductor 177 and battery 178to ground thereby operating relay 128 and opening the switch 127. Whenswitch 127 opens,

the holding circuit through relay 166 is broken, which allows relay 166to release and return to its normal position.

In a similar mannerthe total attenuation between line sections 5 and 7can be decreased in db steps as long as pointer 68 remains over contact77.

Alarm relays and circuits When all the attenuation units 21 to 27inclusive have been removed from between line sections 5 and 7 by theope-ration of relays 31 to 37 inclusive, the circuit from ground throughbattery 178, conductor 177, relay 145, conductor 183 and switches 191 to197 inclusive on relays 31 to 37 inclusive to ground is broken, by theopening of switches 91 to 197 inclusive. This causes relay 145 toelease, which opens switch 144, preventing the operation of the selectorswitches when contact 77 is closed, and closes switch 200. Thesubsequent closing of switch 77, by the action of cam 73, completes acircuit from ground through switch 77, conductor 143, switch 200,conductor 201, switch 202 on relay 203, relay 203, conductor 177 andbattery 178 to ground, and also completes another circuit from groundthrough switch 77, conductor 143, switch 200, conductor 201, switch 198on relay 204, relay 204, conductor 177, battery 178 to ground, therebyoperating relays 203 and 204. When relay 204 operates, switch 198 isopened, and switch 232 is closed, thereby completing a circuit fromground through switch 246 on relay 128, switch 234 on relay 235, switch232 on relay 2044, relay 204, conductor 177 and battery 178 to ground,thereby locking up relay 204 in its operated position.

The operation of relay 204 closes switch 205, completing a circuit fromground through switch 205, lamp 206 and battery 178 to ground, therebylighting lamp 206, and also completes a circuit from ground throughswitch 207, switch 208 on relay 209, bell 210 and battery 211 to ground,thereby ringing bell 210. r

W hen desired, the alarm cell 210 may be stopped by closing switch 236on key 123, which completes a circuit from ground through switch 236,relay 209 and battery 178 to ground, thereby operating relay 209. VVhnrelay 209 operates, it is held in that position by the completed circuitfrom ground through battery 178, relay 209, switch 237 on relay 209 and.switch 205 on relay 204 to ground. Relay 209 will remain in its operatedposition until switch 205 is broken by the release of relay 204.

The operation of relay 209 also opens switc 1 238, extinguishing lamp239 and closes switch 240. lighting lamp 241, thereby indicating thatthe relay 209 is in an operated position.

Nhen all the attenuation equalizer units 21 to 27 inclusive have beenconnected between the line sections 5 and 7, due to relays 31 to 37inclusive being released as shown, the circuit from ground throughbattery 178, conductor 177, relay 117, conductor 212 and switches 221 to227 inclusive to ground is broken, by the opening of switches 221 to 227inclusive, which causes relay 117 to release as shown. It subsequentlythe indicator pointer 68 is directly over contact 76 and causes theclosing of contact 76 by the action of cam 73 a circuit is completedfrom ground through switch 76, conductor 80, switch 228, conductor 201and relays 203 and 204, causing these relays 203 and 204 to operate asdescribed above. Due to the opening of switch 116 on relay 117, theoperation of the selector switches, as described above, under control ofthe high contact 76 is prevented.

Relay 84 is energized under control of the A, B and C selectors, as willbe described presently and if the A, B or C selectors fail to functionproperly, relay 84 will be released, since the circuit through switcharms 102 on the C1 selector, 97 on the B2 selector, and 94 on the A4selector will be broken. When relay 84 is released the switches 83, 146and 118 are opened, preventing the operation of the selector circuitswhen the high or low contacts 76 and 77 are closed and thereby preventinthe operation of relays 31 to 37 inclusive when the switch 81 (triggercontact) is closed. Switch 230 on relay 84 closes when relay 84releases. The subsequent operation of switch 81 by cam 72 completes acircuit from ground through switch 81, conductor 82, switch 230,conductor 201 and relays 203 and 204, operating these relays and thealarms as described above.

If an open circuit occurs in the line ML or in the transmission pathfrom line ML through filter 1, equalizer 2, line section 3, transformer4, line section 5, attenuator 6, line section 7, amplifier 8, or in theline section 60 and the associated apparatus between line section 60 andindicating recorder 66, the indicating pointer 68 will return to thezero position over contacting device 78. l/Vhen switch 78 is closed bythe action of cam 73, a circuit will be completed from ground throughswitch 78, conductor 201 and relays 203 and 204, thereby operatingrelays 203 and 204, which causes lamp 206 to light and the alarm bell210 to ring as described above.

Since cam 73 causes the closing of one of switches 76, 77 or 78 every 15seconds, except when the pointer 68 is between switches 76 and 7 7, andsince it is also desirable to have the alarm circuits automaticallyrestore to normal if the indicating pointer moves over contactingdevices 7 6 or 77, it is necessary to keep the alarm circuits fromrestoring, provided switch 78 is closed once in every 15- second cycle.Since as stated above, relay 204 is held operated by the circuit throughswitch 232, this circuit must be opened to re lease relay 204.v Relays128, 203 and 235 are utilized to cause relay 204 to remain in itsoperated position as long as switches 78 and 81 are alternately closedbythe action of cams 7 3 and 72, respectively.

lVhen switch 78 is closed, relay 203 operates as described above. Theoperation of relay 203 closes switch 242, completing a circuit fromground through switch 7 8, conductor 201, switch 242, switch 243 onrelay 235, relay 235, conductor 177 and battery 178 to ground, therebyoperating relay 235. When relay 235-operates, switch 243 opens andswitch 244 closes. When switch 244 closes, .a circuit is completed fromground through battery 178, conductor 17 7, relay 235, switch 244 onrelay 235, and switch 245 on relay 203 to ground, which holds relay 235in its operated position. ,VVhen switch 81 subsequently closes, relay128 is operated as above described. Relay 128, when operated, closesswitch 233, holding relay 235 operated and also opens switch 246, whichbreaks a circuit through relay 203, causing relay 203 to release. Relay203, when released, opens switch 245, which breaks the circuit fromground through switch 245 to relay 235. In this manner relay 235 remainsoperated until relay 128 is released in the manner described above. y

If during the subsequent cycles of the depression of theindicating-pointer 68 by the action of cam 73: and the closing ofswitch.

81 by the action of cam 72,. the relay 203 is and remains. operatedduring the interval in which relay 128 operates and releases undercontrol of switch 81, the switch 247 on relay 235 will complete acircuit from ground, through switch 247, switch 232 on relay 204,

relay 204, conductor 177 and battery 17 8 to ground thereby holding therelay 204 in its operated position. Since relay 235 will release onlyafter relay 128 has released, it will I therefore maintain relay 204 inits operated posit-ion until relay 128 has released. However, when relay128 releases, relay 204 is stillmaintained in'its operated position :bythe circuit referred to above from ground, switch 246 on relay 128,-etc., through relay 204.

If, however, when relay 128 subsequently operates, and the operation ofrelay 128 is not followed by the closing of switch 78, the relay 235,being in its unoperated position, the circuit referred tov above whichholds relay 204 operated will be opened and relay 204 will release,restoring relay 209 to'its unoperated posltion. 1 i Y 1 In asimilarmanner the alarm circuits are held in an operated position whenall the attenuation equalizer units have been inserted betweenlinesections.5 and 7 as long as the high contact 76 and the trigger contact81 are alternately closed by the actionof cams 73 and 72 respectively,by means of the switches described above which are operated by relay117. The alarm circuits will release on the failure of switch 76 toclose after switch 81 has closed. In a similar manner relay 145 controlsthe holding of the alarm circuits in an operated position when allattenuation equalizer units have been removed from between line sections5 and 7 and the low contact 77 and trigger contact 81 periodicallyclose. The alarm circuits are restored to normal 011 the failure ofswitch 77 to close after switch-81 has closed.

In order that an alarm will be given when the A, B and C selectors failto function properly, switches have been provided on relay 84 to preventthe above described operation of the selectors when the high or lowcontacts 76 and 77 are closed and'to cause the trigger contact 81 toclose a circuit through the alarm relays. The function of relay 8 1 isto release when the A selector switch arms 91 to 95 inclusive are in anyposit-ion other than the normal positions shown, when the B selectorswitch arms 96 to 101 inclusive are in any other position than inconnection with one of the first eight selector switch contacts and whenthe G selector switch arms 102 to 106 inclusive are in any positionexcept in contact with the first fourteen selector switch contacts. Whenrelay 84 is released, switch 81 is connected in the circuit with thealarm relays and is disconnected from relays 128 and 56, which resultsin the opening of the circuits described above from the high and lowcontacts 76 and 77 to the selector switch circuits. The circuit throughrelay 84 is from ground through battery 178, conductor 1-77,

relay 84, conductor 179, any one of the fourteen selector switchcontacts 180 of the G1 selector switch, selector switch arm 102,conductor 181, any oneof the eight selector switch contacts 182 on theB2 selector switch,

selector switch arm 97, conductor 139, selector switch contact 140 onthe A4 selector switch and selector switch arm 94 to ground.

In this manner the transmission of current due to the closing of switch81 is transferred from its normal path through "relays 128 and 56 torelays 203, 204 and 235. In this case the relays 203 and 235 do notrelease periodically as described above for the other alarm circuits. Assoon as the selector switches return to their proper positions, so thatrelay 84 is again operated, the current transmitted by the closing ofswitch 81 will operate relay 128 as described above and release relays103 and 235, and the subsequent closingof switch 81 will release thealarm circuits in the manner referred to above. I i

' In order that the indicating pointer 68 shall not be held clamped inany position if the motor should stop and also to prevent the pointer 68from closing contacts 76, 77

or 78 during manual operation of the system, a magnet 2118 and anassociated relay 249 (Fig. 3) are provided to prevent the bar fromcoming in contact with the pointer 68 by the action of cam 7 Relay 2 18is operated by closing switch 250 of hey 123, which completes a circuitfrom ground through switch 250, conduct-or 251, relay 219, conductor 177and battery 178 to ground. Relay 218 is held in its operated position.by a circuit from ground through switch 127 on relay 128, switch 252 onrelay 2-19, relay 2 19, conductor 177 and battery 178 to ground. Whenrelay 2 19 operates, switch closes, completing a circuit from groundthrough battery 1.7 8, conductor 177, switch 253, conductor 25 1, andmagnet 218 to ground. he relay 2-19 and the magnet 248 are, therefore,

held in an operated position until after relay 128 has operated inresponse to current transmitted through relay 128 by the closing ofswitch 81 on the indicating controller.

An additional alarm circuit is employed to indicate the failure of thevoltage source to which the motor 70 is connected. Relay 255 (Fig. 1) isnormally in an operated position. Upon failure of the voltage sourcerelay 255 releases, closing switch 256. When switch 256 closes, acircuit is completed from ground through switch 256, lamp 257 andbattery 258 to ground, thereby lighting lamp 257. Another circuit iscompleted from ground through switch 256, switch 259 on relay 260, relay261 and battery 262 to ground, thereby operating relay 261. lVhen relay261 operates switch 263 closes, completing a circuit from ground throughswitch 263, bell 264 and battery 265 to ground, thereby ringing bell26 1. Switch 266 is also closed by the operation of relay 261,completing a circuit from ground through switcl 266, lamp 267 andbattery 268 to ground, thereby lighting lamp 267. W hen desirable, theringing of bell 26 1 can be stopped by closing switch 269, therebycompleting a circuit through relay 260 and battery 270 to ground. Switch259 is opened and switches 271 and 272 are closed by the operation ofrelay 260. When switch 259 opens relay 261 releases, opening the circuitthrough the bell 261 and the lamp 267. l/Vhen switch 271 closes, acircuit is completed from ground through battery 270, relay 260, switch271. to ground, thereby holding relay 260 in its operated position.lVhen switch 272 closes, a circuit is completed from ground throughswitch 272, lamp 273, battery 271 to ground, thereby lighting lamp 273.The alarm circuit is restored to its normal position by the operation of1'elay'255 which opens switch 256.

Although this invention has been described in connection with certainspecific embodiments it is intended to be limited only by the scope ofthe appended claims.

What is claimed is:

1. :The method of regulating a characteristic of an electrical circuitwhich consists in setting up electrical paths in accordance with thecondition of said characteristic and periodically and only at timesintermediate and differing by an appreciable interval from, the times ofthe successive settin up operations transmitting currents through saidpaths to effect the desired adjustment of said electrical circuit.

2. The method of regulating a characteristic of an electrical circuit,comprising se ting up electrical control paths in accordance with thecondition of said characteristic, periodically changing said paths whensaid condition calls for a change in regulation, and effecting thechange in regulation by sending current impulses through said controlpaths that have been set up, only at times intermediate and differingfrom the times of the successive setting up operations.

3. In combination, means to be regulated, regulating means, means forproducing an indication of the characteristic of said means to beregulated, means for setting up electrical paths in accordance with theindication produced, and means for periodically and only at timesintermediate and difl ering by an appreciable interval from, the timesof the successive setting up operations transmitting currents throughsaid paths to etl'ect the desired adjustment of said regulating means.

4. In a signaling circuit, transmission regulating means thereforcomprising a response element, means for varying the transmission level,and means for controlling said means for varying the transmission levelby said response element, said controlling means setting up electricalpaths and periodically and only at times intermediate and differing byan appreciable interval from, the times of the successive setting upoperations transmitting currents through said paths to eifect thedesired adjustment of said regulating elements.

5. In a signaling circuit, transmission regulating means thereforcomprising a response element, means for varying the transmission level,and means for controlling said varying means comprising means forselectively setting up electrical'paths under control of said responseelement, and means operative in the intervals intermediate thesuccessivesetting up operations to effect the desired adjustment of saidregulating elements.

6. In a signaling circuit, transmission regulating means therefor, saidmeans comprising a response element, means for varying the transmissionlevel, and means for controlling said means for varying the transmissionlevel, said controlling means comprising means automatically operable inresponse to said response element to select electrical paths and meansto transmit currents periodically and within the intervals intermediatethe successive setting up operations through said paths to eilect thedesired adjust-ment of said means for varying the transmission level.

7. In a transmission system, transmission regulating means comprising anelement responsive to different transmission conditions in said system,means for periodically associating said element with the system topermit said element to give a response corresponding to the transmissioncondition of said system, means for adjusting the transmission level ofthe system, electrical response elements for controlling said lastmentioned means, means placing said last mentioned response elementsunder the control of said first mentioned response element when thelatter is associated with said transmission system, and means forcausing said electrical response elements to exercise con trol of saidmeans for adjusting the transmis sion level intermediate the times ofassociation of said first mentioned response element with saidtransmission system.

8. In a regulator system, regulator means adjustable in steps, astep-by-step control system for effecting the adjustment of saidregulator means, including means for automatically stepping the controlsystem to effect an adjustment in the regulator means, a measuringinstrument responsive to electrical variations in a system to beregulated, means under the joint control or" said measuring instrumentand said control system for adj usting said regulator means from anyadjustment to any new adjustment within its range, means automaticallyoperable for rendering said adjusting means inoperative when eitherlimit of said adjustment range is reached, and for giving an alarm, andmeans automatically operable for stopping said alarm and again renderingsaid adjusting means operative when said regulator means requires a newadjustment within its range.

9. In a regulator system, regulator means adjustable in steps, ameasuring instrument responsive to electrical variations in a system tobe regulated, impulse sending means under control of said instrument,stepping means controlled by said impulses for ellecting an adjustmentin the regulator means, de-

pendent in extent upon the number of impulses sent under control or themeasuring instrument, and means automatically operable under control ofsaid stepping means to prevent impulses from being transmitted to saidstepping means when said stepping means fails to function properly.

10. In a regulator system, regulator means adjustable in steps, ameasuring instrument responsive to electrical variations in a system tobe regulated, one-way rotary switches ti L) adapted to change theadjustment of said regulator means in one direction only, other one-wayrotary switches adapted to control the number of steps of said firstmentioned one-way rotary switches to change the adjustment of saidregulator means in the other direction, and impulse sending means undercontrol of said instrument adapted to control said other rotaryswitches. v

11. In a regulator system, regulator means adjustable in steps, ameasuring instrument responsive to electrical variations in a s sterm tobe regulated, one-way rotary switc ies adapted to change the adjustmentof said regulator means in one direction only, other one-way rotaryswitches adapted to control the number of steps of said first mentionedone-way rotary switches to change the adjustment of said regulator meansin the other direction, impulse sending means undercontrol of saidinstrument adapted to set up electrical paths through said rotaryswitches and other impulse sending means under control of saidinstrument adapted to transmit elec trical impulses through saidelectrical paths.

12. In a regulator system, regulator means adjustable in steps, ameasuring instrument responsive to electrical variations in a system tobe regulated, one-way rotary switches adapted to change the adjustmentof said regulator means in one direction only, other one-way rotaryswitches adapted to control the number of steps of said first mentionedone-way rotary switches to change the adjustment of said regulator meansin the other direction, impulse sending means under control of saidinstrument adapted to set up electrical paths through said rotaryswitches and to transmit electrical impulses through said electricalpaths, and means to prevent said impulse sending means from setting upnew paths from said rotary switches and from sending electricalimpulsesthrough said paths when said rotary switches fail to functionproperly.

13. In a regulator system, regulator means adjustable in steps, ameasuring instrument responsive to electrical variations in a system tobe regulated, one-way rotary switches adapted to change the adjustmentof said regulator means in one direction only, other one-way rotaryswitches adapted to control the number of steps of said first mentionedone-way rotary switches to change the adj ustment of said regulatormeans in the other direction, impulse sending means under control ofsaid instrument adapted to set up electrical paths through said rotaryswitches, and means to cause said impulse sending means to operate alarmmeans when said rotary switches fail to function properly.

14. In a regulator system, regulator means adjustable in steps, ameasuring instrument responsive to electrical variations in a system toberegulated, one-wayrotary switches adapted to change the adjustment ofsaid regulator means in one direction only, other one-way rotaryswitches adapted to control the number of steps of said first mentionedone-way rotary switches to change the adjustment of said regulator meansin the other direction, alarm means including impulse sending meansunder control of said instrument adapted to put an alarm circuit in anoperative condition and to maintain said alarm circuit in said operativecondition during the time in which said impulse sending meansperiodically operates and to put said alarm circuit in a non-operativecondition on the failure of said impulse sending means to periodicallyoperate.

'15. In a signaling system, transmission regulating means thereforcomprising a response element, means for varying the transmission level,means for controlling said means for varying the transmission level bysaid response element, comprising stepping mechanism for setting upelectrical paths and periodically transmitting currents through saidpaths to effect the desired adjustment of said regulating elements, andmeans automatically operable under control of said stepping mechanismfor preventing said stepping mechanism from setting up electrical pathsand periodically transmitting currents through said paths to effect anew adjustment of said regulating element when said stepping mechanismfails to function properly.

16. In a regulator system, regulator means adjustable in steps, ameasuring instrument responsiveto electrical variations in a system tobe regulated, one-way step-by-ste rotary switches adapted to change thea justment of said regulator means in either direction, impulse sendingmeans under control of said instrument adapted to rotate said one-wayrotary switches to change the adjustment of said regulator means in onedirection, other one-way rotary switches adapted to set up electricalpaths under control of a single impulse from said measuring instrumentto cause said first mentioned oneway step-by-step rotary switch toautomatically rotate through a definite number of steps to change theadjustment of said regulator means in the other direction.

17. In a regulating system arranged for both automatic and manualoperation, means to be regulated, a plurality of regulating elements, adeflecting member responsive to change of conditions affecting thecharacteristics of said means to be re ulated, means for effectingautomatic operation of said regulating system including a pivoted memberadapted to engage said deflecting member, a periodically operatingmember adapted to actuate said deflecting member through said pivotedmember, a plurality of stationary contacting devices cooperating withsaid deflecting member, connections from said stationary contacts forcontrolling the number of said regulating elements associated With saidmeans to be regulated, and means actuated When said system is placedunder manual control for preventing said periodically operating memberfrom actuating said defiecting member through said pivoted member Whilemaintaining said deflecting member responsive to change of conditionsatfecting the characteristics of said means to be regulated, said lastmentioned means com prising an electromagnet associated With saidpivoted member.

18. In a regulating system, means to be regulated, regulating means,means for producing an indication of the characteristic of said means tobe regulated, means for automatically setting up electrical paths inaccordance with the indication produced, means for transmitting currentsthrough said paths to effect the desired adjustment of said regulatingmeans, means for manually setting up electrical paths to effect anadjustment of said regulating means and for rendering inoperative saidmeans for automatically setting up electrical paths While maintainingthe others of said means in an operative condition.

In Witness whereof, We hereunto subscribe our names this 24th day ofJune, 1929.

ROY W. CHESNUT. DONALD M. TERRY. WALTER F. KANNENBERG.

